1. Field of the Invention
This invention relates generally to intraocular lenses and more particularly to novel accommodating intraocular lenses for implantation within the capsular bag of a human eye from which the natural lens matrix has been removed by an extraction procedure which leaves intact within the eye the posterior capsule and an anterior capsule remnant of the natural lens. The invention relates also to a novel method of utilizing the intraocular lenses in a human eye to provide the patient with accommodation capability responsive to normal ciliary muscle action.
2. Prior Art
The human eye has an anterior chamber between the cornea and the iris, a posterior chamber behind the iris containing a crystalline lens, a vitreous chamber behind the lens containing vitreous humor, and a retina at the rear of the vitreous chamber. The crystalline lens of a normal human eye has a lens capsule attached about its periphery to the ciliary muscle of the eye by zonules and containing a crystalline lens matrix. This lens capsule has elastic optically clear anterior and posterior membrane-like walls commonly referred by ophtalmologists as anterior and posterior capsules, respectively. Between the iris and ciliary muscle is an annular crevice-like space called the ciliary sulcus.
The human eye possesses natural accommodation capability. Natural accommodation involves relaxation and constriction of the ciliary muscle by the brain to provide the eye with near and distant vision. This ciliary muscle action is automatic and shapes the natural crystalline lens to the appropriate optical configuration for focussing on the retina the light rays entering the eye from the scene being viewed.
The human eye is subject to a variety of disorders which degrade or totally destroy the ability of the eye to function properly. One of the more common of these disorders involves progressive clouding of the natural crystalline lens matrix resulting in the formation of what is referred to as a cataract. It is now common practice to cure a cataract by surgically removing the cataractous human crystalline lens and implanting an artificial intraocular lens in the eye to replace the natural lens. The prior art is replete with a vast assortment of intraocular lenses for this purpose.
Examples of such lenses are described in the following U.S. Pat. Nos. 4,254,509, 4,298,996, 4,842,601, 4,963,148, 4,994,082, 5,047,051.
As is evident from the above patents, intraocular lenses differ widely in their physical appearance and arrangement. This invention is concerned with intraocular lenses of the kind having a central optical region or optic and haptics which extend outward from the optic and engage the interior of the eye in such a way as to support the optic on the axis of the eye. My above-listed U.S. Pat. No. 5,047,051, discloses an intraocular lens having a haptic anchor plate, an optic at the longitudinal center of the plate, and resilient haptic loops staked to the ends of the plate.
Up until the late 1980""s, cataracts were surgically removed by either intracapsular extraction involving removal of the entire human lens including both its outer lens capsule and its inner crystalline lens matrix, or by extracapsular extraction involving removal of the anterior capsule of the lens and the inner crystalline lens matrix but leaving intact the posterior capsule of the lens. Such intracapsular and extracapsular procedures are prone to certain post-operative complications which introduce undesirable risks into their utilization. Among the most serious of these complications are opacification of the posterior capsule following extracapsular lens extraction, intraocular lens decentration, cystoid macular edema, retinal detachment, and astigmatism.
An improved surgical procedure called anterior capsulotomy was developed to alleviate the above and other post-operative complications and risks involved in intracapsular and extra-capsular cataract extraction. Simply stated, anterior capsulotomy involves forming an opening in the anterior capsule of the natural lens, leaving intact within the eye a capsular bag having an elastic posterior capsule, and anterior capsular remnant or rim about the anterior capsule opening, and an annular sulcus, referred to herein as a capsular bag sulcus, between the anterior capsule remnant and the outer circumference of the posterior capsule. This capsular bag remains attached about its periphery to the surrounding ciliary muscle of the eye by the zonules of the eye. The cataractous natural lens matrix is extracted from the capsular bag through the anterior capsule opening by phacoemulsification and aspiration or in some other way after which an intraocular lens is implanted within the bag through the opening.
A relatively recent and improved form of anterior capsulotomy known as capsulorhexis is essentially a continuous tear circular or round capsulotomy. A capsulorhexis is performed by tearing the anterior capsule of the natural lens capsule along a generally circular tear line substantially coaxial with the lens axis and removing the generally circular portion of the anterior capsule surrounded by the tear line. A continuous tear circular capsulotomy or capsulorhexis, if performed properly, provides a generally circular opening through the anterior capsule of the natural lens capsule substantially coaxial with the axis of the eye and surrounded circumferentially by a continuous annular remnant or rim of the anterior capsule having a relatively smooth and continuous inner edge bounding the opening. When performing a continous tear circular capsulorhexis, however, the anterior rim is often accidentally torn or sliced or otherwise ruptured, or the inner rim edge is nicked or sliced in a manner which renders the rim prone to tearing when the rim is stressed, as it is during fibrosis as discussed below.
Another anterior capsulotomy procedure, referred to as an envelope capsulotomy, involves cutting a horizontal incision in the anterior capsule of the natural lens capsule, then cutting two vertical incisions in the anterior capsule intersecting and rising from the horizontal incision, and finally tearing the anterior capsule along a tear line having an upper upwardly arching portion which starts at the upper extremity of the vertical incision and continues in a downward vertical portion parallel to the vertical incision which extends downwardly and then across the second vertical incision. This procedure produces a generally archway-shaped anterior capsule opening centered on the axis of the eye The opening is bounded at its bottom by the horizontal incision, at one vertical side by the vertical incision, at its opposite vertical side by the second vertical incision of the anterior capsule, and at its upper side by the upper arching portion of the capsule tear. The vertical incision and the adjacent end of the horizontal incision form a flexible flap at one side of the opening. The vertical tear edge and the adjacent end of the horizontal incision form a second flap at the opposite side of the opening.
A third capsulotomy procedure, referred to as a beer can or can opener capsulotomy, involves piercing the anterior capsule of the natural lens at a multiplicity of positions along a circular line substantially coaxial with the axis of the eye and then removing the generally circular portion of the capsule circumferentially surrounded by the line. This procedure produces a generally circular anterior capsule opening substantially coaxial with the axis of the eye and bounded circumferentially by an annular remnant or rim of the anterior capsule. The inner edge of this rim has a multiplicity of scallops formed by the edges of the pierced holes in the anterior capsule which render the annular remnant or rim prone to tearing radially when the rim is stressed, as it is during fibrosis as discussed below.
Intraocular lenses also differ with respect to their accommodation capability, and their placement in the eye. Accommodation is the ability of an intraocular lens to accommodate, that is to focus the eye for near and distant vision. My U.S. Pat. No. 5,326,347 and certain of the earlier listed patents describe accommodating intraocular lenses. Others of the listed patents describe non-accommodating intraocular lenses. Most non-accommodating lenses have single focus optics which focus the eye at a certain fixed distance only and require the wearing of eye glasses to change the focus. Other non-accommodating lenses have bifocal optics which image both near and distant objects on the retina of the eye. The brain selects the appropriate image and suppresses the other image, so that a bifocal intraocular lens provides both near vision and distant vision sight without eyeglasses. Bifocal intraocular lenses, however, suffer from the disadvantage that each bifocal image represents only about 40% of the available light and the remaining 20% of the light is lost in scatter.
There are four possible placements of an intraocular lens within the eye. These are (a) in the anterior chamber, (b) in the posterior chamber, (c) in the capsular bag, and (d) in the vitreous chamber.
According to one of its aspects, this invention provides improved accommodating intraocular lenses to be implanted within the capsular bag of a human eye which remains in the eye after removal of the natural matrix from the human lens capsule through an anterior capsule opening created by an anterior capsulotomy and preferably by a capsulorhexis. An improved accommodating intraocular lens according to the invention has a central optic and haptics which extend outward from diametrically opposite sides of the optic and are movable anteriorly and posteriorly relative to the optic. In some described lens embodiments, the haptics are joined at their inner ends to the optic by hinge-like junctions referred to herein as hinges, and the anterior/posterior movement of the haptics involves pivotal movement of the haptics at these hinges. In other described embodiments, the haptics are resiliently flexible, and the anterior/posterior movement of the haptics relative to the optic involves resilient flexing or bending of the haptics. In this regard, it is important to note at the outset that the terms xe2x80x9cflexxe2x80x9d, xe2x80x9cflexingxe2x80x9d, xe2x80x9cflexiblexe2x80x9d, and the like are used herein in a broad sense to cover both hinged and resiliently bendable haptics.
Certain of the lens embodiments described herein are referred to as simple plate haptic lenses. These simple plate haptic lenses are intended for use when the capsulotomy procedure utilized in the eye surgery is properly performed and provides an anterior capsule remnant or rim that is not only completely intact and free of splits, tears, and the like at the time of lens implantation but is also likely to remain intact during subsequent fibrosis. Other described lens embodiments are referred to as a plate haptic spring lens. These latter lenses are intended for use in those situations in which the capsulotomy produces an anterior capsular remnant which is not intact or which is not likely to remain intact during fibrosis. Both types of lenses are designed for implantation within a capsular bag of the eye in a position wherein the lens optic is aligned on the axis of the eye with the anterior capsule opening in the bag, and the lens haptics are situated within the capsular bag sulcus in contact with the sulcus wall. The normally posterior side of the lens then faces the elastic posterior capsule of the bag.
The presently preferred lens embodiments of the invention have round optics and haptics joined at their inner ends to opposite edges of the optic by relatively narrow junctions. These junctions occupy only relatively small diametrically opposite edge portions of the optics and leave unobstructed the remaining major circular edge portions of the optic between the junctions. In the preferred lenses described herein, these junctions are hinge junctions about which the haptics are movable anteriorly and posteriorly relative to the optic. These flexible or hinged junctions form a bridge between the optic and the plate haptic which is fixed in position within the anterior and posterior capsules by fibrosis. The bridges are tapered, the widest end being adjacent to the optic. This allows the bridge to slide in and out of the pocket formed by the fibrosed anterior capsular rim and the posterior capsule,and enables the optic to move anteriorly when the plate haptics are subjected to end to end compression.
During a post operative healing period on the order of three weeks, active endodermal cells on the posterior side of the anterior capsular rim cause fusion of the rim to the elastic posterior capsule by fibrosis. Fibrosis occurs about the haptics in such a way that the haptics are effectively xe2x80x9cshrink-wrappedxe2x80x9d by the capsular bag and form radial pockets between the anterior rim and the posterior capsule. These pockets contain the haptics and act to position and center the lens in the eye. The anterior capsular rim shrinks during fibrosis. This shrinkage combined with shrink-wrapping of the haptics causes endwise compression of the lens in a manner which tends to deflect the center of the lens along the axis of the eye relative to the fixated outer haptic ends. The intact fibrosed capsular rim prevents forward deflection of the lens, so that fibrosis-induced deflection of the lens occurs rearwardly to a position in which the lens presses against the elastic posterior capsule and stretches this capsule rearwardly.
Relaxation of the ciliary muscle during normal use of the eye after completion of fibrosis stretches the capsular bag and the fibrosed anterior capsular rim. The rim is stretched to a taut trampoline-like condition in which the rim deflects the lens rearwardly to and holds the lens in a posterior position. In this position of the lens, which is its distant vision position, the lens optic presses rear-wardly against And stretches the elastic posterior capsule. The stretched posterior capsule then exerts a forward bias force on the lens.
The accommodating lenses of the invention are uniquely constructed and arranged to utilize the fibrosed anterior capsular rim, the elastic posterior capsule, the vitreous cavity pressure, and the natural brain-controlled ciliary muscle action of the eye to provide postoperative accommodation for near vision. Thus, when looking at a near object, the brain constricts the ciliary muscle. This relaxes the fibrosed anterior rim, increases vitreous cavity pressure, and compresses the lens endwise in such a way as to effect forward deflection, i.e. accommodation movement, of the lens optic along the axis of the eye to a near vision position. Depending upon the amount of accommodation, accommodation deflection of the lens is produced initially by the increase in vitreous pressure and the forward bias force of the stretched posterior capsule and finally by forward buckling of the lens in response to endwise compression of the lens. Subsequent brain-activated relaxation of the ciliary muscle stretches the capsular bag and the fibrosed anterior capsular rim to return the lens rearwardly toward its distant vision position.
The preferred lens embodiments of the invention have round optics which are sized in diameter to pass through the anterior capsule opening. These preferred lenses are constructed and arranged for anterior accommodation movement of their optics to positions wherein the optics project through the anterior capsule opening to maximize the accommodation range of the lenses.
According to another important aspect of the invention, the ciliary muscle is paralyzed in its relaxed state at the start of surgery and is maintained in this relaxed state during both surgery and post-operative fusion of the anterior capsular remnant or rim to the posterior capsule by fibrosis. The ciliary muscle is thus relaxed by introducing a ciliary muscle relaxant (i.e. a cycloplegic) into the eye. While various cycloplegics may be used, the preferred cycloplegic is atropine because of its relatively long effective period compared to other cycloplegics. The cycloplegic is initially introduced into the eye at the start of surgery to dilate the pupil and paralyze the ciliary muscle in its relaxed state. After surgery, cycloplegic drops are periodically introduced into the eye by the patient during a postoperative healing period of sufficient duration (normally about two to three weeks) to maintain the ciliary muscle in its relaxed state until fibrosis is complete. This drug-induced relaxation of the ciliary muscle prevents contraction of the muscle and immobilizes the capsular bag during fibrosis. By this means, the lens is fixed in position within the eye relative to the retina for distance vision. When the cycloplegic effect wears off and the ciliary muscle can contract again, the contraction causes end to end compression on the plates thus moving the optic anteriorly for near vision. If the ciliary muscle was not maintained in its relaxed state, the muscle would undergo essentially normal brain-induced vision accommodation contraction and relaxation during fibrosis. This ciliary muscle action during fibrosis would not only result in improper formation of the haptic pickets in the fibrose tissue, but also ciliary muscle contraction during fibrosis would compress the capsular bag radially and the lens endwise in such a way as to very likely dislocate the lens from its proper position in the bag.
An accommodating lens according to the invention may have a normal unstressed configuration, such that when deflected from its normal unstressed configuration, the lens develops internal elastic strain energy forces which bias the lens toward its normal unstressed configuration in a manner which aids accommodation. The lens may be generally flat, anteriorly arched, or posteriorly arched in this normal unstressed configuration. One disclosed embodiment of the lens includes auxiliary springs for aiding lens accommodation. Some disclosed lens embodiments have integral fixation means at the haptic ends around which fibrosis of the anterior rim of the capsular bag occurs to fix the lens against dislocation in the eye. Other disclosed embodiments have fixation elements from which the lens proper is separable to permit later removal of the lens for repair or correction and replacement of the lens in its exact original position within the eye.
As noted earlier, the simple plate haptic lens of the invention is designed for use when the anterior capsulotomy performed on the eye provides an anterior capsular remnant or rim that remains intact and circumferentially continuous throughout fibrosis. The plate haptic spring lenses are designed for use when the anterior capsular remnant or rim of the capsular bag is ruptured, that is cut or torn, or is liable to become so during fibrosis. A ruptured capsular rim may be produced in different ways. For example, improper performance of a continuous tear circular capsulotomy, or capsulorhexis, may result in accidental cutting or tearing of the anterior rim. A beer can or can opener capsulotomy, on the other hand, produces an anterior capsular rim which is not intact and has an inner scalloped edge having stress-inducing regions that render the rim very prone to tearing during surgery or subsequent fibrosis. An envelope capsulotomy inherently produces an anterior capsular remnant which is ruptured and not intact.
A ruptured anterior capsular remnant or rim may preclude utilization of a simple plate haptic lens of the invention for the following reasons. A ruptured rim may not firmly retain the lens haptics in the sulcus of the capsular bag during fibrosis, thereby rendering the lens prone to decentration and/or posterior or anterior dislocation. A ruptured capsular rim may be incapable of assuming the taut trampoline-like condition of a non-ruptured rim. If so, a ruptured capsular rim is incapable of effecting full posterior deflection of a plate haptic lens to a distant viewing position against the posterior capsule during and after fibrosis. In fact, a ruptured capsular rim may permit anterior deflection of the lens. In either case, since the power of the lens is selected for each individual patient and is dependent upon their spectacle power, and since good vision without glasses requires the lens optic to be at precisely the correct distance from the retina, a simple plate haptic lens of the invention may not be acceptable for use with a ruptured anterior capsular remnant or rim.
The accommodating plate haptic spring lenses of the invention are designed for use when the anterior capsular remnant or rim of the capsular bag is ruptured. These plate haptic spring lenses are similar to the simple plate haptic lenses but have resilient springs, such as spring loops, at the ends of the plate haptics. When a plate haptic spring lens is implanted in a capsular bag, the haptic springs press outward against the wall of the capsular bag sulcus to fixate the lens in the bag during fibrosis. Fibrosis occurs about the springs in such a way as to effect fusion of the ruptured anterior remnant to the posterior capsule, firm fixation of the springs and hence the haptics in the bag, and posterior deflection of the lenses against the elastic posterior capsule during fibrosis. Brain-induced constriction and relaxation of the ciliary muscle after fibrosis with a ruptured capsular rim effects accommodation of the plate haptic spring lens in much the same way as occurs with the simple plate haptic lens and an intact non-ruptured capsular rim.
While the plate haptic spring lenses of the invention are designed for use with a ruptured anterior capsular remnant or rim, these lenses can also be utilized with an intact rim. A plate haptic spring lens also compensates for improper lens placement in the eye with one end of the lens situated in the capsular bag and the other end of the lens situated in the ciliary sulcus of the eye. In this regard, an advantage of the plate haptic spring lenses of the invention over the simple plate haptic lenses resides in the fact that the spring lenses eliminate the need to have on hand in the operating room both a simple plate haptic lens for use with an intact capsular rim and a plate haptic spring lens as a substitute for the plate haptic lens in the event the rim is ruptured during surgery.
Another advantage of the plate haptic spring lenses over the simple plate haptic lenses of the invention resides in the fact that the haptic spring lenses permit an optic of larger diameter than those of simple plate haptic lenses whose optic diameters will normally be restricted to the range of 4-7 mm. Thus, the haptic spring lenses rely on the haptic springs rather than the capsular remnant or rim to retain the lenses in position during fibrosis. As a consequence, these lenses may be used with a capsular remnant or rim of reduced radial width or a capsular rim which is slit or torn, both of which rim types provide an anterior capsule opening of larger effective size than those possible with a simple plate haptic lens. A larger anterior capsule opening, in turn, permits a larger optic diameter which offers certain opthalmological benefits. According to one aspect of this invention, such a large opening is provided after fibrosis is complete by using a laser to slit the anterior capsular rim radially or cut the rim circumferentially to enlarge the opening.
A further aspect of the invention concerns a novel method of utilizing an accommodating lens of the invention to provide accommodation in a human eye whose natural lens matrix has been removed from the lens capsule by a procedure involving anterior capsulotomy of the natural lens. The method may be utilized to replace a natural lens from which a cataract has been removed and to correct a refractive error in the eye of a patient who previously wore glasses in order to enable the patient to see well without glasses. For example, the invention can can be utilized to correct refractive errors and restore accommodation to persons in their mid-40""s who require reading glasses or bifocals for near vision by replacing the clear non-cataractous crystalline lens matrix of their eyes with an accomodating intraocular lens according to the invention. According to the method of utilizing a plate haptic spring lens of the invention, the anterior capsular remnant or rim of the capsular bag is slit radially or cut to enlarge the anterior capsule opening after fibrosis is complete to permit the use of a lens with a relatively large diameter optic larger than 6 or 7 mm.